The invention relates to pigmentary solid solutions comprising copper phthalocyanine (Pigment Blue 15; C.I. 74160) as host and other blue to violet pigments as guests. Preferred hosts are the xcex1 (Pigment Blue 15:1), xcex2 (Pigment Blue 15:3) and xcex5 (Pigment Blue 15:6) crystal forms of copper phthalocyanine, especially the xcex5 crystal form. Monophase solid solutions are preferred.
The invention also relates, furthermore, to dispersions comprising these solid solutions as pigment particles and pigment derivatives as rheology improvers. Preferred dispersions of solid solutions in the xcex5 crystal lattice may be used in particular to prepare colour filters for liquid-crystal displays (LCDs) which in comparison to existing colour filters have an improved transmission window at 445xc2x110 nm.
The correct position and the absolute value of the transmission window are the most important parameters for colour filters. There is a desire for high transmission in the wavelength range surrounding the light emission, coupled with as high as possible an absorption for different-coloured light. Normally, trichromatism is achieved by using one blue, one red and one green filter. These filters must be highly transparent, homogeneous and able to be prepared in a very uniform layer thickness.
Many blue filters are known and in some cases are available commercially. Some of them contain xcex5 copper phthalocyanine (C.I. Pigment Blue 15:6) and carbazole violet (C.I. Pigment Violet 23). It has been found, however, that these filters are unable entirely to satisfy the present-day requirements. The aim of the invention is therefore to improve the blue filter.
It has repeatedly been disclosed that copper phthalocyanine (crude or in the xcex1 phase) is easily convertible into its xcex2 crystal form, for example in U.S. Pat. No. 2,556,728 by salt grinding with a solvent, in EP-0 803 545 by dry grinding followed by solvent treatment, in EP-0 808 878 by dry grinding with a solid binder in an inert atmosphere, and in WO-99/54410 by dry or aqueous grinding followed by conditioning.
On the other hand, GB-1,411,880 and JP-A-04/252 273 describe the conversion of xcex1 copper phthalocyanine first of all into a mixture of xcex1 and xcex5 copper phthalocyanine in a ball mill and then into pure xcex5 copper phthalocyanine by treatment with solvents at only moderately elevated temperature. These results are, however, hardly reproductible.
U.S. Pat. No. 4,135,944 explains that the formation of xcex2 or xcex5 copper phthalocyanine is dependent not only on shear force, solvent and temperature but also on the presence of a suitable phthalocyanine derivative which determines the formation of the xcex5 crystal phase.
Also apparently showing themselves to be determinants of the crystal phase, according to JP-A-48/76 925, are chlorinated copper phthalocyanines, which are processed together with pure xcex1 copper phthalocyanine to give a mixture whose x-ray diffraction pattern is very similar to that of xcex5 copper phthalocyanine.
JP-A-09/95 638 and JP-A-08/44 056 describe the use in blue colour filters of physical mixtures of xcex1 and xcex5 copper phthalocyanine and, respectively, of xcex1 copper phthalocyanine and dioxazine violet.
JP-A-61/266 471 discloses that the salt kneading of a copper phthalocyanine leads to the R or xcex2 form depending on whether it takes place in the presence or absence of a colourless reaction product of an aromatic isocyanate with an aliphatic amine.
JP-A-07/198 925 describes a 10% liquid dispersion of xcex5 copper phthalocyanine, SiO2 particles (xe2x80x9camorphous fumed silicaxe2x80x9d) and dioxazine violet in N-methylpyrrolidone. However, no solid solution is formed: in contrast, the x-ray powder diagram of a dispersion in accordance with example 1 clearly contains the characteristic signals of xcex5 copper phthalocyanine and those of dioxazine violet separately alongside one another.
The invention also differs in a number of important points from the applications WO-01/04215, WO-01/09252 and JP-A-2000/281924, still unpublished at the priority date. Surprisingly, unwanted phase transformations of copper phthalocyanine in the course of salt grinding may be prevented by adding pigments from a selection of classes. Even more surprisingly, solid solutions are obtained which exhibit improved coloristic properties.